The invention relates to a motor, a fan, and a magnetic bearing assembly thereof, and in particular to a motor, a fan, and a magnetic bearing assembly thereof with characteristics of less abrasion, low noise level, low costs, and longer lifetime.
A conventional motor comprises a shaft, a rotor, and a bearing. The rotor is disposed on the shaft and supported by the bearing, enabling the rotor to rotate smoothly.
Conventional bearings include ball bearings, sleeve bearings, dynamic bearings, and magnetic bearings.
The structure of the ball bearing, however, is weak and susceptible to impact. When the motor with the ball bearing operates, the balls are rolling at high speed and producing excessive noise. The ball bearing requires a higher degree of accuracy, thus increasing manufacturing costs.
A sleeve bearing is formed by mixing and sintering bronze powder, iron powder, nickel powder, lead powder and other metal powders. Lubricant is applied into the pores of the bearing. When the motor operates, lubricant exudes from the bearing such that the rotor rotates in the lubricant. This type of bearing can sustain higher impact than the ball bearing, and manufacturing costs are also reduced. In a motor utilizing the sleeve bearing, however, the lubricant evaporates into gas as the bearing operates over long periods. As a result, the shaft directly contacts the bearing such that friction is produced therebetween. Furthermore, nitrides can possibly form at the ends of the bearing, causing damage and excessive noise. In addition, dust in the air may be drawn into the center of the motor during operation, contaminating the lubricant surrounding the bearing, increasing the noise level and occluding moving parts. Furthermore, since the gap between the bearing and the shaft is small, the efficiency in starting the motor is reduced.
A dynamic bearing is a variation of the sleeve bearing. This type of bearing comprises an inner wall with two annular arrays of V-shaped grooves formed therein, preventing lubricant evaporation. Formation of the grooves on the inner side of the dynamic bearing, however, requires precise manufacturing. Thus, the manufacturing cost is higher than other types of bearings. Moreover, the dynamic effect is not achieved at low speeds, such that performance of the dynamic bearing is substantially the same as a sleeve bearing.
To solve the above problems, a magnetic bearing is disclosed in U.S. Pat. No. 6,414,411. A rotor, a stator, and a balance plate are combined in such way that attraction is generated between the rotor and the balance plate. In this structure, however, the magnetic bearing does not disclose a radial supporting structure, and consequently, the shaft and the bearing may collide during operation, reducing product life of the motor and producing excessive noise.
Furthermore, other patents such as Japan No. S55-36635 (4), Japan No. S64-39926, Japan No. H05-146109, Japan No. S58-083552, U.S. Pat. No. 6,265,798, U.S. Pat. No. 5,507,629, U.S. Pat. No. 5,840,070, U.S. Pat. No. 3,934,950, U.S. Pat. No. 3,663,075, U.S. Pat. No. 4,340,260, U.S. Pat. No. 5,894,181, U.S. Pat. No. 5,280,208, and U.S. Pat. No. 5,019,738, disclose similar structures with the same magnetic polarity designed at a shaft of a rotor and a stator base, thereby the like poles produce repulsive force therebetween such that repulsive force suspends the shaft in the stator base without direct contact. The repulsive force, however, may be diminished if the position of the shaft is offset by external force or driving force during operation, the imbalance can cause the shaft to contact or be expelled from the stator base.
In addition, another U.S. Pat. No. 5,561,335 discloses additional magnets attached to two ends of the magnet of the rotor, providing magnetic balance of the shaft, as shown in FIG. 7 in U.S. Pat. No. 5,561,335. During operation, however, if the magnet is disposed at an incorrect attractive angle with an incorrect moment arm of the magnet, the additional magnet may be adversely frozen due to magnetic attraction, and thus operation is interrupted.
Thus, collisions between the shaft and the bearing may easily occur in conventional motors. This produces excessive noise, shortens product life, and can interrupt normal motor operation. Hence, it can be seen, the magnetic bearing is still in an experimental stage, and is not yet ready for mass production.